Have you found out exactly where the gas is leaking from ? If it's from under the hood area, you may be lucky enough to replace a hose or a gasket. With that said - If it's leaking further back under the car it's most likely leaking from a gas line or the tank itself.
Most times a gas leak is best fixed by a mechanic. It can get to be pretty involved - it usually involves draining the gas tank of gas, (removing it) washing it out (all to prevent a fire hazard) and filling it with air or water to find hole in order to fix it. Then it's a matter of repairing the hole.
Be sure to remember the "remove it" part before filling it with water - if you don't, you'll have more problems than a gas leak.
oil leak
unleaded gas.
When owning a car, it is important to know and remember the gas tank size. The 1996 GMC Jimmy has a gas tank that holds up to 19 gallons of gas.
digital cluster may need replaced
in the gas tank
check your engine
did you check the starter or the gas flow?
It wont shift because its leaking fluid.
unleaded, 89 or higher for a vortec.
I belive it is 19 gallons
May have to take the truck to a certified speedometer repair shop
could be a fuse out